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1.
M. G. Abrahamyan 《Astrophysics》2008,51(3):357-371
A vortical mechanism for the collimation and acceleration of astrophysical jets is proposed on the basis of exact solutions
of the hydrodynamic equations in a homogeneous gravitational field taking viscosity into account. Velocity profiles in the
form of a jet structure with a uniformly rotating trunk whose pressure decreases in time, and longitudinal and converging
radial flows of matter, are examined. Because of the radial flow, the angular velocity of the trunk and the velocity of the
longitudinal flow of matter can accelerate exponentially or in the manner of an “explosive” instability. Flows of this type
have low energy dissipation and can serve as unique channels for the acceleration and collimation of jet eruptions from young
stars, as well as from active galactic nuclei and quasars.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 431–444 (August 2008). 相似文献
2.
The vortex structure of the “npe” phase of neutron stars with a 3P2 superfluid neutron condensate of Cooper pairs is discussed. It is shown that, as the star rotates, superfluid neutron vortex
filaments described by a unitary ordering parameter develop in the “npe” phase. The entrainment of superconducting protons
by the rotating superfluid neutrons is examined. The entrainment effect leads to the appearance of clusters of proton vortices
around each neutron vortex and generates a magnetic field on the order of 1012 G. 3P2 neutron vortex filaments combine with quark semi-superfluid vortex filaments at the boundary of the “npe” and “CFL” phases.
At the boundary of the “Aen” and “npe” phases, they combine with 1S0 neutron vortex filaments. In this way, a unified vortex structure is formed. The existence of this structure and its collective
elastic oscillations explain the observed oscillations in the angular rotation velocity of pulsars. 相似文献
3.
Philip Hardee Yosuke Mizuno Ken-Ichi Nishikawa 《Astrophysics and Space Science》2007,311(1-3):281-286
A new general relativistic magnetohydrodynamics (GRMHD) code “RAISHIN” used to simulate jet generation by rotating and non-rotating
black holes with a geometrically thin Keplarian accretion disk finds that the jet develops a spine-sheath structure in the
rotating black hole case. Spine-sheath structure and strong magnetic fields significantly modify the Kelvin-Helmholtz (KH)
velocity shear driven instability. The RAISHIN code has been used in its relativistic magnetohydrodynamic (RMHD) configuration
to study the effects of strong magnetic fields and weakly relativistic sheath motion, c/2, on the KH instability associated with a relativistic, γ=2.5, jet spine-sheath interaction. In the simulations sound speeds up to
and Alfvén wave speeds up to ∼0.56c are considered. Numerical simulation results are compared to theoretical predictions from a new normal mode analysis of the
RMHD equations. Increased stability of a weakly magnetized system resulting from c/2 sheath speeds and stabilization of a strongly magnetized system resulting from c/2 sheath speeds is found. 相似文献
4.
The superfluid core (“npe” phase) of a neutron star, consisting of superfluid neutrons, superconducting protons, and normal
electrons, is considered. The Gibbs thermodynamic potential of a superconducting proton vortex in a proton superconductor
of the second kind, interacting with the normal core of a neutron vortex of radius r ≪ λ parallel to it (λ is the depth of
penetration), is calculated. It is shown that under this assumption, the capture by the core of only one vortex turns out
to be energetically favored. The force exerted on the proton vortex by the entrainment current, always directed toward the
core, is found. The corresponding force for a proton antivortex is directed outward toward the outer boundary of the neutron
vortex. It is shown that the fluctuational formation of a vortex-antivortex pair is possible at a large distance from the
core under the action of the entrainment current. Under the action of the entrainment current, the antivortex travels outward,
while the vortex remains inside the neutron vortex. It is shown that the formation of new proton vortices is possible only
in the region in which the entrainment magnetic field strength is H(ρ) > Hcl (Hcl is the first critical field).
Translated from Astrofizika, Vol. 42, No. 2, pp. 225–234, April–June, 1999 相似文献
5.
M. G. Abrahamyan 《Astrophysics》2008,51(2):163-180
A vortical mechanism for generation of astrophysical jets is proposed based on exact solutions of the hydrodynamic equations
with a generalized Rankine vortex. It is shown that the development of a Rankine vortex in the polar layer of a rotating gravitating
body creates longitudinal fluxes of matter that converge toward the vortex trunk, providing an exponential growth in the angular
rotation velocity of the trunk and a pressure drop on its axis. The increased rotational velocity of the vortex trunk and
the on-axis pressure drop cease when the discontinuity in the azimuthal velocity at the surface of the trunk reaches the sound
speed. During this time, ever deeper layers of the gravitating body are brought into the vortical motion, while the longitudinal
velocity of the flow along the vortex trunk builds up, producing jet outflows of mass from its surface. The resulting vortices
are essentially dissipationless.
Dedicated to the 100-th birthday of Academician V. A. Ambartsumyan
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Translated from Astrofizika, Vol. 51, No. 2, pp. 201–218 (May 2008). 相似文献
6.
The superfine structure of the jet formation region in the radio galaxy M87 has been investigated. An accretion disk and high-
and low-velocity jet and counterjet components have been identified. The high-velocity bipolar outflow is ejected from the
central disk region, a nozzle 4 mpc in diameter, while the low-velocity one is ejected from a ring 60 mpc in diameter and
14 mpc in width. The low-velocity plasma flow is a hollow tube with a built-in helix. The observed helical structure of the
high-velocity jet is determined by precession. The components of the structure, its disk and bipolar outflow, suggest solid-body
rotation. Ring currents and aligned magnetic fields are generated in them under the action of an external magnetic field.
The bipolar outflows are ejected coaxially but in opposite directions—along and opposite to the disk field. As a result, the
jet flow accelerates, while the counterjet one decelerates. This causes the extent of the region of radiative cooling of the
ejected relativistic electrons in the counterjet to decrease and maintains their “afterglow” at large distances in the jet.
The high collimation of the rotating flows is determined by their interaction with the environment. 相似文献
7.
Equations for the dynamics of a rotating two-component neutron star are derived in the framework of the general theory of
relativity. The density of neutron vortex filaments is expressed in terms of the angular momentum density of the superfluid
neutrons in the “npe” phase of the neutron star. It is shown that a theory of the relaxation of the angular velocity of pulsars
must include corrections associated with the deviation of g00 from unity, which is a consequence of the curvature of space. 相似文献
8.
The superconducting proton condensate in the “npe” phase of a neutron star is considered. It is shown to be a type II superconductor
in the outer layer of the “npe” phase and a type I superconductor in the inner layer. Relaxation times are found for elastic
scattering of normal relativistic electrons from the magnetic fields of proton vortex clusters in the case of a type II superconductor
and elastic scattering from the magnetic field at the center of a neutron vortex in the case of a superconductor of the first
kind. The dynamical relaxation times obtained for the angular velocity of the pulsar PSR 0833—45 vary, as a function of the
density of the layers taking part in the relaxation process, within a fairly wide range: from several hours to l09 years. This means that the characteristic times of variation of pulsar angular velocity may be observed to lie in the indicated
time range.
Translated from Astrofizika, Vol. 40, No. 4, op. 497–506, October–December, 1997. 相似文献
9.
A magnetic field model is constructed for the extremely slow rotator γEqu based on measurements of its magnetic field over
many years and using the “magnetic charge” method. An analysis of γEqu and of all the data accumulated up to the present on
the magnetic field parameters of chemically peculiar stars leads to some interesting conclusions, of which the main ones are:
the fact that the axis of rotation and the dipole axis are not parallel in γEqu and the other slowly rotating magnetic stars
which we have studied previously is one of the signs that the braking of CP stars does not involve the participation of the
magnetic field as they evolve “to the main sequence.” The axes of the magnetic field dipole in slow rotators are oriented
arbitrarily with respect to their axes of rotation. The substantial photometric activity of these CP stars also argues against
these axes being close. The well-known absence of sufficiently strong magnetic fields in the Ae/Be Herbig stars also presents
difficulties for the hypothesis of “magnetic braking” in the “pre-main sequence” stages of evolution. The inverse relation
between the average surface magnetic field Bs and the rotation period P is yet another fact in conflict with the idea that
the magnetic field is involved in the braking of CP stars. We believe that angular momentum loss involving the magnetic field
can hardly have taken place during evolution immediately prior “to the main sequence,” rather the slow rotation of CP stars
most likely originates from protostellar clouds with low angular momentum. Some of the slowly rotating stars have a central
dipole magnetic field configuration, while others have a displaced dipole configuration, where the displacement can be toward
the positive or the negative magnetic pole.
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Translated from Astrofizika, Vol. 49, No. 2, pp. 251–262 (May 2006). 相似文献
10.
Pulsed-power technology and appropriate boundary conditions have been used to create simulations of magnetically driven astrophysical
jets in a laboratory experiment. The experiments are quite reproducible and involve a distinct sequence. Eight initial flux
tubes, corresponding to eight gas injection locations, merge to form the jet, which lengthens, collimates, and eventually
kinks. A model developed to explain the collimation process predicts that collimation is intimately related to convection
and pile-up of frozen-in toroidal flux convected with the jet. The pile-up occurs when there is an axial non-uniformity in
the jet velocity so that in the frame of the jet there appears to be a converging flow of plasma carrying frozen-in toroidal
magnetic flux. The pile-up of convected flux at this “stagnation region” amplifies the toroidal magnetic field and increases
the pinch force, thereby collimating the jet. 相似文献
11.
Luis C. Ho 《Astrophysics and Space Science》2005,300(1-3):219-225
I summarize the main observational properties of low-luminosity AGNs in nearby galaxies to argue that they are the high-mass
analogs of black hole X-ray binaries in the “low/hard” state. The principal characteristics of low-state AGNs can be accommodated
with a scenario in which the central engine is comprised of three components: an optically thick, geometrically accretion
disk with a truncated inner radius, a radiatively inefficient flow, and a compact jet. 相似文献
12.
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards
the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet
“threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. 相似文献
13.
M. G. Abrahamyan 《Astrophysics》2008,51(4):526-543
A class of exact vortical solutions of the hydrodynamic equations for compressible media (single component or two-phase) is
examined, taking viscosity and a gravitational field into account. Velocity profiles that have the structure of a vortex with
a uniformly rotating, low-pressure, low-density trunk and a converging radial flow of matter are analyzed. These flows have
low energy dissipation and can easily occur under natural conditions.
Translated from Astrofizika, Vol. 51, No. 4, pp. 617–632 (November 2008). 相似文献
14.
Jean-Claude Pecker 《Journal of Astrophysics and Astronomy》1997,18(4):323-333
Still more shocking than the metaphysical assumption of some initial singularity, is the constant insistence upon the so-called
cosmological principle of “homogeneity” and “isotropy” of the Universe. Observations do contradict this principle. And to
me, the inhomogeneous, fractal at least on a certain scale range, of the distribution of matter is in itself an important
cosmological fact, hitherto almost neglected. Moreover difficultties as to the applicability of the second principle of thermodynamics,
observations of abnormal redshifts, etc., are casting large doubts not only upon the standard cosmological models, but even
on the interpretation of the observed redshift as due solely to a universal expansion. 相似文献
15.
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards
the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet
“threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet.
* This paper has previously been published in Astrophysics and Space Science, vol. 310:3–4. 相似文献
16.
The Solar Electron Proton Telescope on board the twin STEREO spacecraft measures electrons and ions in the energy range from
30 to above 400 keV with an energy resolution better than 10%. On 22 February 2010 during a short interval of 100 minutes,
a sequence of impulsive energetic electron events in the range below 120 keV was observed with the STEREO-A/SEPT instrument.
Each of the four events was associated with a type III radio burst and a narrow EUV jet. All the events show nearly symmetric
“spike”-like time profiles with very short durations ≃ 5 min. The estimated electron injection time for each individual event
shows a small time delay between the electron spike and the corresponding type III radio emission and a close coincidence
with an EUV jet. These observations reveal the existence of spike-like electron events showing nearly “scatter-free” propagation
from the Sun to STEREO-A. From the time coincidence we infer that the mildly relativistic electrons are accelerated at the
same time and at the same location as the accompanying type III emitting electrons and coronal EUV jets. The characteristics
of the spikes reflect the injection and acceleration profiles in the corona rather than interplanetary propagation effects. 相似文献
17.
R. E. Falco 《Solar physics》2006,234(2):213-242
We offer a new viewpoint that can explain some of the recently obtained high-resolution observations of granules and faculae.
Examining the data of Scharmer, Gudiksen, Kiselman et al. (2002) we observe many granules undergo an evolution that results in faculae emerging from within their boundaries, and
moving towards and into intergranular lanes. These faculae have a characteristic hairpin substructure. The evolving morphology
can be closely described by a fluid dynamic instability we call the “vortex/shear layer” (VSL) interaction. It occurs in all
granules whose underlying structure has vorticity when they emerge into the photosphere through the sub-photospheric turbulent
boundary layer (SPTBL). The VSL results in the creation of vortices from the distributed vorticity of the SPTBL. The subsequent
stretching of these vortices results in high amplification of vorticity, and the concurrent high amplification of the background
magnetic field. Magnetic field lines spiral around the vortices, as well as being stretched along their axis. Thus, the VSL
is also the origin of a coherent local dynamo. The spiral sheathing of high magnetic flux results in a simple explanation
for the “hot wall” effect. The VSL also creates the “dark lanes” observed by Lites, Scharmer, Berger et al. (2004) and groupings of bright hairpins/vortex sheet ensembles, which look like the ribbon faculae (Berger, Rouppe van der
Voort, Lofdahl
et al., 2004). The SPTBL results in emerging tilted granules, which when combined with the VSL create the three-dimensionality
which Lites, Scharmer, Berger et al. (2004), also observed. Both the VSL and the SPTBL result, on average, in a west side bias of hairpin faculae and granular
three-dimensionality.
An erratum to this article is available at . 相似文献
18.
V. N. Melnik A. A. Konovalenko V. V. Dorovskyy H. O. Rucker E. P. Abranin V. N. Lisachenko A. Lecacheux 《Solar physics》2005,231(1-2):143-155
The results of observations of solar decametric drift pair bursts are presented. These observations were carried out during
a Type III burst storm on July 11–21, 2002, with the decameter radio telescope UTR-2, equipped with new back-end facilities.
High time and frequency resolution of the back-end allowed us to obtain new information about the structure and properties
of these bursts. The statistical analysis of more than 700 bursts observed on 13–15 July was performed separately for “forward”
and “reverse” drift pair bursts. Such an extensive amount of these kind of bursts has never been processed before. It should
be pointed out that “forward” and “reverse” drift pair bursts have a set of similar parameters, such as time delay between
the burst elements, duration of an element, and instant bandwidth of an element. Nevertheless some of their parameters are
different. So, the absolute average value of frequency drift rate for “forward” bursts is 0.8 MHz s−1, while for “reverse” ones it is 2 MHz s−1. The obtained functional dependencies “drift rate vs. frequency” and “flux density vs. frequency” were found to be different
from the current knowledge. We also report about the observation of unusual variants of drift pairs, in particular, of “hook”
bursts and bursts with fine time and frequency structure. A possible mechanism of drift pairs generation is proposed, according
to which this emission may originate from the interaction of Langmuir waves with the magnetosonic waves having equal phase
and group velocities. 相似文献
19.
In this paper we study the evolution of a LRS Bianchi I Universe, filled with a bulk viscous cosmological fluid in the presence
of time varying constants “but” taking into account the effects of a c-variable into the curvature tensor. We find that the only physical models are those which “constants” G and c are growing functions on time t, while the cosmological constant Λ is a negative decreasing function. In such solutions the energy density obeys the ultrastiff
matter equation of state i.e. ω = 1. 相似文献
20.
R. Presura V. V. Ivanov Y. Sentoku V. I. Sotnikov P. J. Laca N. Le Galloudec A. Kemp R. Mancini H. Ruhl A. L. Astanovitskiy T. E. Cowan T. Ditmire C. Chiu W. Horton P. Valanju S. Keely 《Astrophysics and Space Science》2005,298(1-2):299-303
An experimental simulation of planetary magnetospheres is being developed to investigate the formation of collisionless shocks
and their effects. Two experimental situations are considered. In both, the solar wind is simulated by laser ablation plasmas.
In one case, the “solar wind” flows across the magnetic field of a high-current discharge. In the other, a transverse magnetic
field is embedded in the plasma flow, which interacts with a conductive obstacle. The ablation plasma is created using the
“Tomcat” laser, currently emitting 5 J in a 6 ns pulse at 1 μm wavelength and irradiance above 1013 W/cm2. The “Zebra” z-pinch generator, with load current up to 1 MA and voltage up to 3.5 MV produces the magnetic fields. Hydrodynamic modeling
is used to estimate the plasma parameters achievable at the front of the plasma flow and to optimize the experiment design.
Particle-in-cell simulations reveal details of the interaction of the “solar wind” with an external magnetic field, including
flow collimation and heating effects at the stopping point. Hybrid simulations show the formation of a bow shock at the interaction
of a magnetized plasma flow with a conductor. The plasma density and the embedded field have characteristic spatial modulations
in the shock region, with abrupt jumps and fine structure on the skin depth scale. 相似文献